1. Field of the Invention
The present invention relates to a position detecting apparatus which obtains an image of an object with an imaging unit for detecting the position in an actual space of the object, and a method of correcting data in the position detecting apparatus.
2. Description of the Related Art
There has been developed a vehicle vicinity monitoring apparatus for obtaining images of one object with two imaging units mounted on a vehicle, for example, either measuring the distance up to the object based on the parallax between the obtained images, or measuring the position in an actual space of the object with respect to the vehicle, and informing the driver of whether there is an obstacle ahead of the vehicle or not (see Japanese Laid-Open Patent Publication No. 2003-216937).
In this invention, assuming that the coordinates of the object in an actual space are defined as (Xn, Yn, Zn) and that a perspective transformation model is used, the coordinates (x, y) in the two-dimensional image obtained by each of the imaging units are calculated by equations (1), (2) below, where F is a camera parameter.x=F·Xn/Zn  (1)y=F·Yn/Zn  (2)
F is obtained by an equation (3) below, where f is a focal length of the imaging unit, and p is a pixel pitch of the imaging unit.F=f/p  (3)
Generally, each of the imaging units has its individual differences in an actual focal length and an actual pixel pitch as errors for design values. Thus, the correct position in an actual space of the object cannot be calculated without correction of the errors.